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When switching from one turbulence model to another which is using different transport equations/parameters, and when monitors of turbulent parameters have been defined, the solver will give an error similar to this:

Error: Cell_Function_Values: unrecognised function: production

or

primitive error: unrecognised function: turbulent

This is due to the solution monitors, which no longer have access to the turbulent parameters used by the previous turbulence model. Examples of this occurrence are the switching of an existing solution from RANS to LES or from SA to k-e or k-w and vice-versa.
Check in the Solution->Monitor menu whether any of your surface or volume monitors are using undefined turbulent parameters. If so, change the turbulence parameter to one in the drop-down list, which is refreshed once the turbulence model has been changed.